1. Field of the Invention
A method and apparatus to drill multiple branch wells from a main generally vertical hole.
2. Description of the Prior Art
In situ leach mining that employs either a single injection and recovery (producer) well or separate injection and producer wells are known. This invention relates to those types employing separate injection and producer wells wherein each of the injection and/or producer wells may have multiple branches.
The two known closest prior art references dealing with multiple branch wells can be found in U.S. Pat. No. 4,222,611 issued Sept. 16, 1980, to W. C. Larson et al entitled "In-Situ Leach Mining Method Using Branched Single Well for Input and Output," and the U.S. Pat. No. 4,249,777 issued Feb. 10, 1981, to W. C. Larson et al entitled "Method of In-Situ Mining." Each of these references is concerned with an in situ method of leach mining wherein branch wells are drilled from the surface to extend from the bottom of a generally vertical well. In the latter reference, there are rows of separate injection and recovery wells. The U.S. Pat. No. 4,222,611 utilizes a single generally vertical main well which acts as both the injection and recovery well and would not be as relevant hereto as a consequence.
The present invention relates to a refinement of the method set forth in the mentioned invention which uses a series of rows of separate injection and recovery wells. The refinement provides for the use of a template made up as a drilling guide, a floating collar, and an internal indexing dog. This allows the branch wells to be drilled from the surface in the proper direction so that they extend from the lower end of the main cased well. It also allows the branch wells to be cased and cemented so that there is no leakage of the leachant material except at designated perforations in the branches.